I agree with sonoran; it's much easier to use grub2 to dual-boot. You can install grub2 on /dev/sdb - this way as sonoran said, it won't mess with your window installation on /dev/sda - as root:
and change the boot order from the BIOS to use /dev/sdb first. When you boot Fedora, update grub.cfg, as root:
grub2-mkconfig -o /boot/grub2/grub.cfg
it should detect the window installation on /dev/sda and add an entry to the grub menu to allow you to boot it.
FWIW, I've using grub2 to dual-boot Linux and Windows for years, it usually works without any problems.
About upgrading, you can always try upgrading first, if it doesn't work you can do a clean install instead (when doing a clean install you should point the installer to install grub on /dev/sdb).